This is a PhaseI/II trial of TNFR:Fc in patients with Polyarticular Juvenile Rheumatoid Arthritis who have failed conventional 2nd line therapy. In the initial portion of the study, all patients will receive 0.4 mg/kg/dose of TNFR:Fc, twice weekly. All responders will enter part two of the study, and be randomized to receive placebo or TNFR:Fc for 4 months or until a flare occurs.